GENERAL ZOOLOGY 



Rhabdite 



Gland cell 



Rhabdite cell 



Flame cell 



Gland cell 



Sensory cell 



Epidermal 

 epithelium 



Basement membrane 



Transverse 

 muscle fiber 



Longitudinal 

 muscle fiber 



- Nerve fiber 

 Mesenchyme 



Formative cell 



Dorsoventral 

 muscle fiber 



Excretory duct 



Gut muscle fiber 



Gastrodermal 

 epithelium 



Fig. 11.9. Diagrammatic representation of the cellular structure of a planarian, as seen in a 

 lona;itudinal section. 



The gastrodermal cells, of endodermal origin, line the enteron and function 

 in digestion. It has been demonstrated that digestion occurs chiefly if not 

 entirely in food vacuoles within these cells, and also that the gastrodermal 

 cells store most of the food reserves. 



Other Turbellaria. The foregoing account refers almost excl.usively to 

 fresh-water planarians, representatives of the order Tricladida. The marine 

 triclads are much like those of fresh water, with the diff^erences involving 

 chiefly modifications of the reproductive system. The terrestrial triclads are 

 large forms living in the upper layers of soil or upon vegetation in warm, 

 moist, tropical habitats. In temperate climates they .sometimes occur in 

 greenhouses, into which they have been introduced, probably from the tropics. 



The order Rhabdocoela, recognized by the straight, "rod-shaped" gut 

 (Fig. 11.10), contains turbellarians, mostly of small size and thus not so 

 favorable for study as planarians, although they are abundant in fresh water. 

 Some have the mouth and pharynx in the middle of the ventral surface, as in 



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